Field of the Invention
The present invention relates to an organic semiconductor crystalline film, a weak oriented epitaxy growth preparation method for preparing the same, and an organic film electronic device such as organic transistor and organic phototransistor comprising the organic crystalline film prepared by the weak oriented epitaxy growth method.
Background Art
In recent years, organic semiconductor materials with high carrier mobility properties and exhibit great potential in the markets of information displays, integrated circuits, photovoltaic cells and sensors. The high carrier mobility property is mainly reflected by organic semiconductor single crystal. The “Physical Vapor Growth” for preparing an organic semiconductor single crystal was reported firstly by Kloc et al., Journal of Crystal Growth, 1997, 182, 416-427.
However, the devices in the practice are required generally to be integrated, and organic semiconductor materials are usually used in the form of films in the devices. Therefore, the “Vapor Phase Deposition” facilitating the preparation of films of a large size becomes a primary method to prepare organic semiconductor polycrystalline films at present. The major controlling factors of single domains polycrystalline films of a large size prepared by vapor phase deposition method are the increase of film growth temperature and the chemical modification of surface (Nature, 2001, 412, 517-520). Because there is no oriented relationship between the organic film prepared by vapor phase deposition method and the substrate, the grain boundary defects can not be controlled effectively, and therefore the carrier mobility of thus prepared organic semiconductor polycrystalline film is lower than that of its single crystal by one order or more. Actually, in the early stage, the preparation technique of controlling the oriented relationship between an organic film and a substrate borrows ideas from the preparation methods of inorganic semiconductor films, in which organic molecular beam epitaxy (OMBE) is a representational one.
In general, the organic molecular beam epitaxy means a technology for growing an organic crystal with a commemsurable modulation and non-commemsurable modulation relationship on a single crystal substrate on the surface of the single crystal substrate (Chem. Rev., 1997, 97, 1793-1896), wherein a relatively low growth temperature is adopted in the early stage, and the sizes of crystals are small, usually about tens of nm, and the organic molecule are grown generally by lying on the substrate; recently, room temperature and high temperature growth methods are employed in the organic molecular beam epitaxy growth, resulting in the increase of crystal sizes, but the organic molecule are grown generally by lying on the substrate, too (Appl. Phys. Lett., 1999, 75, 187-189).
Since an organic molecule is in a geometric form, the epitaxy growth theory of inorganic film cannot be applied directly to the preparation of organic films, and the organic polycrystalline films prepared by this method are not continuous. The oriented polytetrafluoroethylene film method was first employed by Wittman et al. (Nature, 1991, 352, 414-417) to achieve an “Oriented Epitaxy Growth (OEG)” of polymer crystals and organic molecule crystals, which is called herein as “Strong Oriented Epitaxy Growth (SOEG)”. Because of the strong interaction between polytetrafluoroethylene and the epitaxially grown polymer and organic molecules, the molecules in an oriented epitaxially grown crystal are generally arranged parallel to the substrate. As for organic semiconductor, the property of high carrier mobility in the crystal is in the direction of larger inter-molecule π-π interaction. Therefore, as compared with molecular vapor phase deposited film, a better property of carrier mobility is not obtained by the organic semiconductor polycrystalline film grown by polytetrafluoroethylene oriented epitaxy growth method (Thin solid films, 1998, 333, 272; Chem. Mater., 2001, 13, 1341-1348).